Electrolytic conversion of acidic compounds



United States Patent 3,193,484 ELECTROLYTIC CONVERSICN 0F ACIDIC COMPUUNDS William K. T. Gleim, Island Lake, and Elmars Bremanis, Park Ridge, 111., assignors to Universal Oil Products Company, Des Plaines, Iil., a corporation of Delaware No Drawing. Filed Sept. 15, 1961, Ser. No. 138,282 9 Claims. (Cl. 204-79) This invention relates to an improvement in the electrolytic conversion of acidic compounds and more particularly to a novel method of reducing the voltage requirements of the process.

Processes for the electrolytic conversion of acidic compounds have heretofore been proposed in the art. One of the disadvantages of these processes is the ever increasing polarization of the electrodes. The voltage has to be increased to overcome this. However, increasing the voltage is accompanied by a decrease in current yield, thereby increasing the cost of the process. Increase of the current also results in undesired side reactions. Accordingly, there is a definite need for an improvement in the process to eliminate these objections.

The electrolytic conversion of mercapto compounds, for example, is exemplified by the regeneration of used alkali metal hydroxide solutions containing mercaptides as described in Yabroff et al. Patent 2,140,194, Gaylor Pat ent 2,654,706 and others. This process is described in further detail in a paper entitled Electrolytic Regeneration of Treating Solutions, by Zandona and Ripple, which paper was presented at the Seventeenth Mid-Year Meeting of the American Petroleum Institutes Division of Refining at San Francisco, California, on May 14, 1952. A later paper, entitled Economic Aspects of the ADC Electrolytic Mercaptan Process, was presented by Miller and Fiske at the regional meeting of the Western Petroleum Refineries Association in Alma, Michigan, in June of 1954.

A modification of the electrolytic conversion process is described in Miller Patent 2,856,353. In this modification the electrochemical conversion of mercaptides to disulfides is effected in the presence of the reversible system of ferrocyanide-ferricyanide.

While the references described above are directed to the regeneration of used alkali metal hydroxide solutions, it is understood that the improvement of the present invention is used in any electrolytic process for the conversion of acidic compounds and particularly of mercapto compounds. An example of another use of such a process is the conversion of mercaptans, either alone or dissolved in an organic substrate such as hydrocarbon distillate. For example, sour hydrocarbon distillate, including gasoline, kerosene, jet fuel, etc. is subjected to electrolytic conversion to convert the mercaptans contained in the hydrocarbon distillate into disulfides. In another embodiment the present invention is used for the oxidation of hydrogen sulfide and salts thereof such as ammonium sulfide, sodium sulfide, potassium sulfide, etc., either as such or in admixture with hydrocarbon gases, hydrocarbon liquids, water, etc. Other acidic compounds also are converted by the present process including, for example, phenols, cresols, xylenols, etc. These processes are efiected in substantially the same manner as describedin detail in the references hereinbefore set forth.

Any suitable electrolytic system may be employed. In the system described in the publications referred to above, the electrolyzer consists of 60 electric cells in series, through which the spent or used caustic soda solution is passed and is regenerated by an applied direct electric current. The electrodes are nickel plated cast iron, 24" to 36" square by 1" thick, separated by rubber gasketedvulcanized asbestos diaphragms. Each unit consists of an anode oxidation plate and a cathode hydrogen plate separated by an asbestos diaphragm. Each plate has a hole in each corner through which the caustic flows. The spent caustic enters the lower port and flows upward and diagonally to the top port before it enters the anode outlet header. A similar set of ports is provided for the cathode hydrogen plates, which permit circulation of spent caustic solution and release of hydrogen gas. When the electrolyzer plates separated by diaphragms are sealed together, the holes form four channels throughout the entire length of the cell.

The electrolytic cell described in detail in the Yabroif et al. patent referred to above is of cylindrical type and contains a rotatable cylindrical anode. This patent also states that a series of alternating positive and negative electrode plates in rectangular cell also has given satisfactory results.

The conversion of mercaptide ions to disulfides is believed to proceed according to the following equation.

2RS RSSR+2 electrons 1) In the regeneration of used caustic solutions, water is present and the water is decomposed into oxygen as expressed in the following equation:

2 0 2 The anode reaction may be written as follows:

4OH O +2H O+4 electrons (3) The electrolytic conversion of sodium mercaptides to disulfides is expressed in the following equation. Also shown below is the equation for the regeneration of the sodium mercaptides to sodium hydroxides.

In the embodiment described above, the oxygen required for the conversion is generated in situ. In some cases the mercaptide solutions contain entrained oxygen and the oxygen either may be removed or may be allowed to remain in the charge to the electrolytic cell. In still another embodiment, oxygen from an extraneous source may be supplied to the electrolytic cell to furnish the oxygen required for the conversion of the mercapto compound. This embodiment is particularly desirable when substantially all of the anode current is utilized to effect the electro-chemical conversion of the mercaptide ion and the available current will not be used for the decomposition of the water.

The electrolytic conversion may be effected at any suitable temperature which may range from 0 C. to C. or higher and preferably from about 15 to about 50 C. The electrical current required for the process will depend upon the concentration of mercapto compounds in the charge to the electrolytic cell. In the process described in the above publications, it is presumed that 240 volts 3-phase AC. power is available. The power required for the conversion of 225 pounds per day of mercaptan sulfur is estimated to be 63 kilowatts. For the conversion of 500 pounds per day of mercaptan sulfur the power required is estimated to be 136 kilowatts.

When applied to the treatment of a hydrocarbon distillate containing mercaptans, the process of the present invention may be used in various arrangements. When the hydrocarbon distillate comprises gasoline, it generally is desirable to remove as much of the mercaptans as practical from the gasoline, and this is accomplished by first treating the gasoline with an alkaline solution.

The alkaline solution containing the extracted mercaptans then is converted electrically as described herein. The extracted gasoline still contains a minor concentration of mercaptans and this gasoline also may be treated hydroxide.

is understood that other suitable solvents may be used ina subjected to treatment'with an alkaline reagent. A preferred reagent comprises anaqueous solution of an alkali metal hydroxide such as sodium hydroxide (caustic), potassium hydroxide, etc. Other alkaline solutions include aqueous solutions of lithium hydroxide, rubidium hydroxide, cesiurnhydroxide, etc., although, in general, these hydroxides are more expensive and therefore generally are not preferred for commercial use. A preferred alkaline solution is an aqueous solution of from about 1% to about 50% and more preferably 5% to by weight concentration of sodium hydroxide or potassium While aqueous solutions are preferred, it

eluding, for example, alcohols, ketones, etc., or mixtures thereof, either as such or diluted with water.

In accordance with the present invention, electrolytic conversion of acidic compounds is effected in the presence of a phthalocyanine compound. As hereinbefore set forth, this results in a reduction in the polarization of the electrodes and accordingly in a decrease in the voltage requirements. This in turn results in a reduction in the cost of the process and also in reducing side reactions which would occur at the increased voltage which otherwise would be required.

In one embodiment the present invention relates to an improvement in a process for the electrolytic conversion of an acidic compound, which comprises effecting said electrolytic conversion in the presence of a phthalocyanine compound.

In a specific embodiment the present invention relates to an improvement in a process for the regeneration of used alkaline reagent, which comprises effecting said electrolytic regeneration in the presence of cobalt phthalo cyanine sulfonate. H

In still another specific embodiment the present invention relates to an improvement in the electrolytic sweetening of a sour hydrocarbon fluid, which comprises effecting said sweetening in the presence of vanadium phthalo cyanine carboxylate.

From the above embodiments it will be seen that the electrolytic conversion is improved by effecting the same in thepresence of a phthalocyanine compound. Any suit able phthalocyanine compound may be used in the present invention and preferably comprises a metal phthalocyanine. Particularly preferred metal phthalocyanines include cobalt phthalocyanine and vanadium phthalocyanine. Other metal phthalocyanines include iron phthalocyanine, copper phthalocyanine, nickel phthalocyanine, molybdenum phthalocyanine, chromium phthalocyanine, tungsten phthalocyanine, etc. The metal phthalocyanine, in general is not readily .soluble in aqueous solvents and, therefore, when used in an aqueous alkaline solution or for ease of compositing with a solid carrier, a derivative of the phthalocyanine is preferred. A particularly preferred derivative is the sulfonated derivative. Thus, an especially preferred phthalocyanine compound is cobalt phthalocyanine sulfonate. Such a compound is available commercially and comprises cobalt phthalocyanine disulfonate and also contains cobalt phthalocyanine monosulfonate Another preferred compound comprises vanadium phthalocyanine sulfonate. These compounds are obtained from any suitable source or are prepared in any suitable manner as, for example, by reacting cobalt or vanadium phthalocyanine with 2550% fuming sulfuric acid. While the sufonic acid derivatives are preferred, it is understood 'cured inthe range of about 0.8 v. to 0.0 v.

that other suitable derivatives may be employed. Other derivatives include particularly the carboxylated derivative which may be prepared, for example, by the action of trichloroacetic acid on the metal phthalocyanine or by the action of phosgene and aluminum chloride. In the latter reaction the acid chloride is formed and may be converted to the desired carboxylated derivative by conventional hydrolysis.

As hereinbefore set forth, the phthalocyanine compound may be used as a solution in an alkaline reagent or other charge being subjected to electrolytic conversion. In another embodiment the phthalocyanine compound may be composited with a solid support and utilized as finely divided particles entrained in the alkaline solution or other charge. 'In this embodiment the phthalocyanine compound is composited with any suitable support which preferably comprises activated charcoal, coke or other suitable forms of carbon. In some cases the support may comprise silica, alumina, magnesia, etc., or mixtures thereof. The solid catalyst is prepared in any suitable manner. In one method, preformed particles of the solid support are soaked in a solution containing the phthalocyaninecompound, after which excess solution is drained off and the composite is used as such or is subjected to a drying treatment, mild heating, blowing'with air, hydrogen, nitrogen,'etc., or successive treatments using two or more of these operations, prior to use; In other methods of preparing the solid composite, a solution of the phthalocyanine compound may be sprayed or poured over the particles of the solid support, or such particles may be dipped, suspended, im-

mersed or otherwise contacted with a solution of the phthalocyanine compound. The concentration of phthalocyanine compound in the composite may range from 01% to 10% by weightor more of the composite.

The phthalocyanine compound is used in any suitable concentration. Generally this is used in comparatively lowconcentrations which may range from 1 to parts per million of phthalocyanine compound based upon the charge to the electrolytic converter. However, it

is understood that a larger concentration of phthalocyanine may be used when desired and may range up to 5000 parts per million or more.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

7 Example I was 0.003 M n-heptyl mercaptan and 1 N NaOH. The

mercaptan was prepared as a methanolic solution and added in this manner to the sodium hydroxide. The

solution contained 2% by volume of methanol.

The evaluations were made using a Sargent Model XXI recording polarograph. The polarograms were se- The change of current output at continuously varied applied voltage was recorded. r

A control sample of the test'solution was first evaluated in the manner described above. In the potential range used, nosubstantial oxidation of the mer'captan occurred at the platinum electrode. Other experiments indicated that no rapid mercaptan oxidation occurs unless the voltage 15 increased to a region where decomposition of the electrolyte occurs.

The platinum Wire electrode then was coatedwith cobalt phthalocyanine monosulfonate by dipping the electrode into a solution of the phthalocyanine compound. When evaluated in the same manner as described above, the current rose to 120 microamperes, indicating a high rate of mercaptan oxidation.

The above data show that coating of the platinum wire electrode considerably increased the oxidation of mercaptans at the same voltage range.

Example II This evaluation was made using the same equipment described in Example I except that the applied potential was kept constant at -O.25 v. and a solution containing one part per million of cobalt phthalocyanine monosulfonate in dilute sodium hydroxide was included in the test solution. When evaluated in the above manner, the test solution containing the phthalocyanine compound resulted in a rapid current rise to about 120 microamperes in about 1 /2 minutes. This indicates that the phthalocyanine compound was adsorbed rapidly on the platinum wire electrode. Accordingly, this run demonstrates the improved conversion of the mercaptan compound when the electrolysis is efiected in the presence of the phthalocyanine compound.

Example III Thermally cracked gasoline containing hydrogensulfide and mercaptans is first prewashed with a 5% aqueous sodium hydroxide solution to remove the hydrogen sulfide. The prewashed gasoline then is treated with 20% aqueous potassium hydroxide solution containing parts per million of vanadium phthalocyanine sulfonate. The potassium hydroxide solution containing mercaptides and phthalocyanine compound then is subjected to electrolytic conversion in a filter-press electrolytic cell as described in the publications hereinbefore set forth. In a plant charging 5000 barrels per day of cracked gasoline, approximately 215 pounds of mercaptan sulfur are removed and converted in the manner described above. The regenerated potassium hydroxide solution then is recycled for further use in treating sour cracked gasoline.

Example IV A fractionator overhead in a refinery contains ammonia and hydrogensulfide. Upon cooling the vapors, ammonium sulfide is formed. Water is supplied during the condensing and dissolves the ammonium sulfide. The water containing ammonium sulfide then is subjected to electrolytic oxidation in the presence of cobalt phthalocyanine carboxylate in the manner described hereinbefore. This serves to oxidize the ammonium sulfide and permits removal of the sulfur from the water. The

6 treated water then is reused to absorb additional arrimonium sulfide from the fractionator overhead vapors.

We claim as our invention:

1. A process for the electrolytic oxidation of a sulfur compound which comprises passing a direct current through an alkaline electrolyte bath containing a compound selected from the group consisting of mercaptans, mercaptides, hydrogen sulfide and salts thereof in contact with an anode and a cathode, said electrolyte bath also containing a phthalocyanine compound.

2. A process for the electrolytic oxidation of a sulfur compound which comprises passing a direct current through an aqueous alkaline electrolyte bath containing a compound selected from the group consisting of mercaptans, mercaptides, hydrogen sulfide and salts thereof in contact with an anode and a cathode, said electrolyte bath also containing a phthalocyanine compound.

3. A process for the electrolytic oxidation of a mercapto compound which comprises passing a direct current through an aqueous alkaline electrolyte bath containing a mercapto compound in contact with an anode and a cathode, said electrolyte bath also containing a phthalocyanine compound.

4. A process for the electrolytic oxidation of a mercaptide which comprises passing a direct current through an aqueous alkali metal hydroxide solution containing a mercaptide in contact with an anode and a cathode, said solution also containing a phthalocyanine compound.

5. A process for the electrolytic oxidation of a mercap tide which comprises passing a direct current through an aqueous caustic solution containing a mercaptide in contact with an anode and a cathode, said solution also containing a phthalocyanine compound.

6. The process of claim 5 further characterized in that said compound is cobalt phthalocyanine sulfonate.

7. The process of claim 5 further characterized in that said compound is vanadium phthalocyanine sulfonate.

8. The process of claim 5 further characterized in that said compound is cobalt phthalocyanine carboxylate.

9. The process of claim 5 further characterized in that said compound is vanadium phthalocyanine carboxylate.

References Cited by the Examiner UNITED STATES PATENTS 2,654,706 10/53 Gaylor 204-153 2,794,768 6/57 Brooks 204-79 WINSTON A. DOUGLAS, Primary Examiner.

JOHN R. SPECK, JOHN H. MACK, Examiners. 

1. A PROCESS FOR THE ELECTROLYTIC OXIDATION OF A SULFUR COMPOUND WHICH COMPRISES PASSING A DIRECT CURRENT THROUGH AN ALKALINE ELECTROLYTE BATH CONTAINING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF MERCAPTANS, MERCAPTIDES, HYDROGEN SULFIDE AND SALTS THEREOF IN CONTACT WITH AN ANODE AND A CATHODE, SAID ELECTROLYTE BATH ALSO CONTAINING A PHTHALOCYANINE COMPOUND. 